Thermal regulating system



Nov. 6, 1962 w. J. BRowN THERMAL REGULATING SYSTEM 3 Sheets-Sheet 1Original Filed April 7, 1950 8 le 24 52 40 TEMPERATURE C F/gl.

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THERMAL REGULATING SYSTEM Original Filed April '7, 1950 5 Sheets-Sheet 2INV EN TOR Walter J Brown ATTORNEYS Nov. 6, 1962 w. J. BROWN THERMALREGULATING SYSTEM 3 Sheets-Sheet 3 Original Filed April 7, 1950 TEMPER/vTURE Co Pfg/2.

INV ENT OR Waltemfo Wn United States `Patent ntice 3,062,999 PatentedNov. 6, 1962 3,062,999 THERMAL REGULATIN G SYSTEM Walter J. Brown,Stamford, Conn., assignor to Vectrol Engineering Inc., Stamford, Conn.,a corporation of Delaware Original application Apr. 7, i950, Ser. No.154,547, now Patent No. 2,842,345, dated July 8, 1958. Divided and thisapplication Apr. 30, 1958, Ser. No. 732,069

7 Claims. (Cl. S20- 35) This application is a division of my co-pendingapplication Serial No. 154,547, tiled on April 7, 1950, entitled ThermalRegulating System, now U.S. Patent 2,842,345.

This invention relates to thermal regulating or heat governing systemsfor controlling the operation of heating and/or cooling equipment of anykind, such, for example, as equipment for heating and/or coolingbuildings, vehicles, incubators, constant temperature baths,airconditioning equipment, refrigerators, water heaters and otherhousehold appliances, such as, ironers, irons, clothes driers, ovens,furnaces, industrial processing heaters and also heating and/ or coolingequipment of the heat pump type,

One object of the invention is to provide a thermal regulating systemwhich is controlled by the variation of dielectric constant withtemperature of certain materials, such as Rochelle salt, barium orstrontium titanate and mixtures or compounds thereof, which will bereferred to for convenience as temperature-sensitive dielectrics.

Another object of the invention is to provide a thermal regulatorcomprising a capacitor incorporating a temperature-sensitive dielectrichaving a Curie point, at which a maximum dielectric constant occurs, inthe neighborhood of a temperature which it is desired to control.

Another object of the invention is to provide a thermal regulatingsystem controlled by a resonant circuit including a capacitor having atemperature-sensitive dielectric.

Another object of the invention is to provide a thermal regulatingsystem which provides continuous control or modulation of the flow ofheat by the variation in a capacitance which incorporates atemperature-sensitive dielectric.

Another object of the invention is to provide such continuous control bymeans of an electric power controller or converter, the output of whichis continuously controlled by the variation in a capacitanceincorporating a temperature-sensitive dielectric. A further object is tocontrol such converter by means of a phase-shifting network whichincludes a capacitor incorporating a temperature-sensitive dielectric.

A further object of the invention is to provide continuous control ofthe tlow of heat by means of an electric space discharge device, theoutput of which is controlled by a capacitor having atemperature-sensitive dielectric, said capacitor preferably forming partof a phase-shifting network.

A further object of the invention is to provide means for adjusting thecontrolling temperature by adjustment of an independent electricalconstant, such as an inductance, capacitance, resistance or a voltage,current or a phase angle in the electrical control circuit.

A further object of the invention is to provide means for adjusting thecontrolled temperature by means of an adjustable heater mounted adjacentthe temperaturesensitive dielectric so as to establish a predetermineddifference between the temperatures of the dielectric and of itssurroundings.

A further object of the invention is to use a temperature sensitivedielectric in a system as above described such that the Curie point isjust above the temperature which it is desired to maintain, wherebydecrease in tem- CII perature Will decrease the capacitance (and viceversa) and will thus advance the output phase angle of a phaseshiftingnetwork and so increase the output of the converter controlling aheating system, and especially to select Rochelle salt or abarium-strontium titanate of approximately :20 ratio as a suitablematerial for the control of room heating.

A further object of the invention is to select a temperature-sensitivedielectric material such that the Curie point is just below thetemperature which it is desired to maintain in a cooling system, wherebyincrease in temperature will `decrease the capacitance (and vice versa)and will thus advance the output phase angle of a phase-shifting networkand so increase the output of the converter controlling the coolingsystem, and especially to select Rochelle salt or a barium-strontiumtitanate having approximately a 70:30 ratio as a suitable material forthe control of room cooling.

A further object of the invention is to provide a combined heating andcooling system, controlled by a capacitor having a temperature-sensitivedielectric with its Curie point at the desired temperature, whereby theoutput of the converter is increased when the temperature departs eitherupwards or downwards from the desired temperature, thus increasing therate of heat transfer, together with thermostatically controlledswitching means to reverse the flow of heat at the Curie point so as toprovide a heating system below the Curie point and a cooling systemabove the Curie point.

A further object of the invention is to control heating and/or coolingequipment in accordance with the approximate average of the temperaturesat several points, by providing a capacitor with a temperature-sensitivedielectric at each point and electrically connecting them to the samecontrol system. Such capacitors may be installed at various pointswithin a building, or alternatively one or more such capacitors may beinstalled outside the building to anticipate and compensate for changesin outdoor temperature.

A further object of the invention is to provide a system of continuouscontrol of the fuel or other power input to a heating or cooling systemby temperature-senstive dielectric means.

A further object of the invention is to provide a system of continuouscontrol, by temperature-sensitive dielectric means, of the transfer ofheat from or to a heatexchanging medium which is heated or cooled byother means.

A further object of the invention is to provide a system of continuouscontrol of the transfer of heat from or to a heat exchanging medium bytemperature-sensitive dielectric means, together with a system ofintermittent control of the fuel or other power input to provide theheating or cooling for said medium.

A further object of the invention is to provide a temperature-sensitiveelectrical phase-shifting network including a capacitor having atemperature-sensitive dielectric.

A further object of the invention is to provide a control system foralternative temperature ranges by means of a plurality oftemperature-sensitive capacitors having different Curie points, and aswitch for selecting same.

A further object of the invention is to provide a temperature-limitingdevice for an electrolytic cell such as a storage battery in which theelectrical input power is continuously controlled to limit maximumtemperature in the cell.

A further object of the invention is to control the high frequencyoutput of an electric power converter supplying power to an induction ordielectric heating device, or to an ultrasonic energy device, wherebythe maximum temperature of a body or fluid under treatment iscontinuouSly controlled.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims, taken in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a graph plotting dielectric constant versus temperature fora temperature-sensitive dielectric;

FIGURE 2 shows a family of similar graphs for a diiferent dielectricmaterial;

FIGURE 3 is a generic block diagram of a thermal regulating system;

FIGURE 4 is a specific form of a heat governing system, particularlyadapted for room heating and/or cool- FIGURE 5 is a vector diagram ofthe voltage vectors obtainable from the thermal regulator incorporatedin the system of FIGURE 4;

FIGURE 6 is another modication of a heat governing system which has aninverted sense of operation;

FIGURE 7 is a still further modification of a heat governing systemwhich also has an inverted sense of operation;

FIGURE 8 is a vector diagram of the voltage vectors obtainable from thephase-shifting network used in the thermal regulator of FIGURE 7;

FIGURE 9 is a graph of dielectric constant versus temperature of atemperature-sensitive dielectric and showing a family of curves obtainedby varying a superimposed direct current voltage on the dielectric;

FIGURE l is a modification of a thermal regulator, such as that usedwith FIGURE 6;

FIGURE 11 is a modiiication of the heat energy controller where-in aplurality of temperature-sensitive capacitors may be used to control thetemperature of a liquid bath; and

FIGURES l2 and 13 are modification of heat energy controllers whereinheat is produced as an unwanted byproduct and a temperature-sensitivecapacitor is used to limit the maximum permissible temperature.

FIGURE 1 shows the relation between the initial free dielectric constantko of Rochelle salt and temperature, at a low iield strength, asillustrated by W. G. Cady in Piezoelectricity. McGraw-Hill, 1946, onpage 557, Fig. 119. The curve exhibits a sharp maximum of dielectricconstant at a temperature of 24 degrees centigrade, which is generallyreferred to as a Curie point, indicated by the letter c in FIGURE 1. Idraw attention to the fact that this Curie point occurs at a convenientroom temperature of 24 degrees centigrade or approximately 75.2 degreesFahrenheit, and that the dielectric constant falls away very rapidlyindeed for the iirst degrees centigrade or 9 degrees Fahrenheit belowand above the Curie point. Accordingly, I conveniently control theheating of a room during the winter and/ or the cooling of a room duringthe summer by means of a thermal regulator comprising a capacitor havingRochelle salt as its dielectric, in conjunction with other elements tobe described.

I control the heating of a room during winter by means to be describedwith starts the flow of heat into the room as the temperature falls to apredetermined value below 24 degrees centigrade, and continuouslyincreases the iiow as the temperature falls still further, so that theroom temperature becomes stabilized at a temperature such, for example,as 22 degrees centigrade (71.6 degrees Fahrenheit) as illustrated by apoint a in FIGURE l. Alternatively, I control the cooling of a roomduring the summer by starting the ow of heat out of the room as thetemperature rises to a predetermined value above 24 degrees centigradeand continuously increaess the ow las the temperature rises stillfurther so that the room temperature is stabilized at a temperaturesuch, for example, as 26 degrees centigrade (78.8 degrees Fahrenheit) asillustrated by point b in FIGURE l.

The temperatures hereinbefore specified are the temperatures of thedielectric of the Rochelle salt capacitor itself and, if it is desiredto stabilize the room temperal ture at a lower value, I may provide asmall heater adjacent to said condenser which will raise its temperatureby the required amount above the ambient temperature in the room, thusdepressing the room temperature by the same amount.

However, it is frequently desirable to provide for a wider range oftemperature control, and I may do this by using an alternative materialas the dielectric of my capacitor. It is necessary, in order to have asensitive temperature controlling system, to choose a material having arapid variation of dielectric constant over the desired temperaturerange. For the purpose of this application, I will define a dielectricmaterial of which the dielectric constant, otherwise known as thepermittivity, varies with temperature, as a temperature-sensitivedielectric, and I will dene a capacitor having such a dielectric as atemperature-sensitive-capacitor.

FIGURE 2 shows the relation between the dielectric constant and thetemperature for a series of materials known as the barium-strontiumtitanate series, as illustrated by Prof. Willis Jackson in The Journalof the Institution of Electrical Enginners (London), vol. 94, lPart III,No. 27, January 1947, page 9, Figure 5. It will be seen that the Curiepoint depends upon the relatiwe barium-strontium ratio, and I mayaccordingly choose a material from this seriesor a m-aterial having someintermediate ratio--to suit the particular application.

For instance, for the control of room heating, I may choose abarium-strontium titanate having a Curie point at 40 degrees centigrade,corresponding to a bariumstrontium titanate ratio of approximately :20,in conjunction with other equipment to be described, which increases theiiow of heat into the room as the temperature falls below the Curiepoint, so as to stabilize the temperature at any desired value between35 degrees and 20 degrees centigrade. For the control of room cooling Imay choose a barium-strontium titanate having a Curie point of l0degrees centigrade, corresponding to a ratio of approximately 70:30, inconjunction with equipment to increase the flow of heat out of the roomas the temperature rises above the Curie point, so as to stabilize thetemperature at any desired value between 20 degrees and 35 degreescentigrade.

In all the arrangements so far described, it has been assumed thatequipment is provided, as described hereinafter, which increases theliow of heat as the temperature moves away from the Curie point, whetherfor heating or for cooling, and I will arbitrarily define this as normalcontrol.

=It is, however, possible to reverse the sense of the control byproviding equipment which I have defined as having inverted control, andwhich will be described hereinafter. In such an inverted control system,the ow of heat is continuously decreased as the temperature moves awayfrom the Curie point. For a heating system with inverted control, Iwould choose, for example, a 70:30 barium-strontium titanate, and sincethe ow of heat is continuously decreased as the temperature rises abovethe Curie point, the temperature may be stabilized at any desired valuebetween 20 degrees and 40 degrees centigrade. For a cooling system withinverted control, I might use an 80:20 bariumstrontium titanate and Imay stabilize the temperature at any desired value between 35 degreesand 20 degrees centigrade.

While I have referred to the flow of heat as being continuouslyvariable, I do not intend that it should be continuously variable overthe whole of the wide ranges of temperature specified above, but onlyover a desired part of such range. For instance, in a heating systemwith inverted control as hereinbefore described, and assuming a desiredtemperature of 25 degrees centigrade, I would arrange for the maximumpossible rate of heat liow from 10 degrees centigrade to say 24 degreescentigrade, followed by a continuous decrease in heat iiow from 24degrees to 26 degrees centigrade, followed by zero or substantially zeroheat iiow at higher temperatures. In this way I may maintain asubstanti-ally constant temperature of 25 degrees plus or minus l degreecentigrade; I have constructed equipment which will regulate thetemperature even more closely than this.

FIGURE 3 illustrates my invention in a generic form, and variouselements of a thermal regulating system are shown in the form of a blockdiagram. The block designated 21 is a thermal regulator comprising acapacitor 22 which will be referred to hereinafter as atemperature-sensitive capacitor since it comprises atemperature-sensitive dielectric 23 and conductive electrodes 24 and 25;the dielectric 23 may comprise Rochelle salt or barium or strontiumtitanate, or a mixture or cornpound of barium or strontrium titanate, orany other dielectric which exhibits a rapid change of dielectricconstant as the temperature is varied above and/or below a desiredvalue.

The most suitable materials are those which are frequently known asferro-electric materials, which include Rochelle salt and the titanateshereinbefore mentioned, since these are characterized ,by a .sharpmaximum of dielectric constant at a particular temperature usuallyreferred to as a Curie point.

The temperature-sensitive capacitor 22 is connected to an impedance 26and the capacitor-impedance circuit so formed is connected toalternating current input means 27 which are provided with terminals 28and 29 for connection to a source of alternating current 32.`Connections are also provided from the alternating current input meansand the capacitor-impedance circuit 22-26 to conductors 30 and 31 whichform the output conductors of the thermal regulator 21. The thermalregulator 21 may conveniently take the form of a phase-shifting networkhaving the temperature-sensitive capacitor 22 as a variablephase-controlling element therein. Alternatively, the thermal regulator21 may comprise an alternating current network having capacitor 22 as anamplitude-controlling element therein.

An electric power controller 33 is provided ywith input terminals 34 and35 for connection to -a source of power 36 which may conveniently beidentical with the alternating current source 32. The flow of electricpower through the electric power controller 33 is controlled in acontinuously variable manner Iby the output of the thermal regulator 2.1by connections 30 and 31 and the electric power so controlled issupplied to the electric power controller output conductors 37 and 38.The electric power controller may conveniently take the form of arectifier comprising one or mor-e space discharge devices such asthyratrons or mercury arc retiiiers provided with control electrodes,the output of which is continuously variable by varying the phase angleof an alternating current voltage applied to said control electrodes, orby varying a rectied alternating current voltage which is lapplied tosaid electrodes preferably in conjunction with an alternating currentvoltage which is phase-displaced in relation to the anode voltagel ofsaid rectifier.

The block 39 in FIGURE 3 represents a heat energy controller, which maycomprise any device or system in, which heat is generatedvand/orabsorbed, transferred on exchanged at a rate which is progressivelygradually controllable by the continuously variable electrical inputwhich is applied to its terminals 40 and 41 from the electric powercontroller 33 through conductors 37 and 38. It may comprise any of theknown electrically operated devices for controlling the iiow of a fueland/or of the air required for its combustion, or alternatively of aheat-containing or heat-exchanging medium such as a hot or cold fluid.

It may comprise, for example, an electrically driven fan or pump forcirculating a heat-containing or heat-exchanging fluid or a fluid fuel,or an electrically driven stoker for a solid fuel, preferably, thoughnot necessarily of a variable speed type driven, for example, by adirect current or universal motor.

Alternatively, the heat energy controller 39 may comprise anelectrically controlled valve or damper for a heat-containing orheat-exchanging fluid or a fluid fuel or for the air required for thecombustion of a fuel; preferably, such valve or damper is of thecontinuously adjustable type. Alternatively, the heat energy controller39 may comprise a device in which heat is created from an electricalinput, for instance, by means of a heating resistor connected toterminals 40 and 41, or by means of a motor-driven heat pump such as `acompressor, for a refrigerator or for a reverse cycle heating system, oralternatively by means of an induction or dielectric heating device inwhich event the electrical input is supplied to terminals 4t) and 41 ata suitable alternating current frequency.

The heat energy controller may alternatively take the form of a devicein which heat is created, sometimes -as an unwanted lby-product, theamount of which it is de-` sired to limit, such for instance as astorage battery of which 4i) and 41 represent the charging terminals, oran ultrasonic transducer device, taking a high frequency electricalenergy input at its terminals 40 yand 41 and c011- verting suchelectrical energy into wanted ultrasonic energy and unwanted heatenergy. In any of the aforesaid arrangements, the temperature-sensitivecapacitor 22 is associated with the heat energy controller 39 so thatits temperature is dependent upon the heat flow produced by said -heatenergy controller. This is not shown in FIG- URE 3, however, it is soshown in FIGURES 7, 11, 12 and 13.

FIGURE 4 illust-rates a Specific form of my invention. The thermalregulator 51 includes a plurality of temperature-sensitive capacitors 52and 4S3 connected in parallel with each other and a switch 54 isprovided so that any one of the fixed capacitors 55, 56, 57 may also beconnected in parallel with the temperature-sensitive capacitor ifdesired. The temperature-sensitive capacitors may be mounted in anydesired position in the space or fluid or body of which it is desired tocontrol the temperature, and the fixed capacitor group may be mounted inany position from which it is convenient to control the desiredtemperature, and all the capacitors may be c011- nected in parallelthrough conductors 58, 59 which may be of any desired length providingthe capacity between said conductors is not high in comparison with thatof said capacitors. Conductor 58 is connected to a terminal 60 of areactor 61, the other terminal 62 of which is connected to analternating current input means 63. Conductor '59 is connected toanother terminal 64 of the alternating current input means 63. Thealternating current input means 63 comprises a transformer having itsprimary 65 connected to input terminals 66 and 67 for connection to analternating current source 32. Across the end terminals 68, 64 of thetransformer secondary 69 there are connected a capacitor `7i) and aresistor 71 in series with each other and with terminal 62 therebetween.An output conductor 72 is connected to an intermediate tap 73 ontransformer secondary 69, and a second Output conductor 74 is connectedto terminal 60.

The thermal regulator as hereinbefore described for use in thisembodiment of my invention has the electrical characteristics of asensitive phase-shifting network of the type described in my copendingpatent application, Serial No. 779,909, tiled Oct. l5, 1947, now issuedas Patent No. 2,524,762 on October l0, 1950, entitled Phase ShiftCircuit, while having the novel feature that the phase angle of theoutput voltage is dependent upon the temperatures of thetemperature-sensitive capacitors 52 and 53 as well,

as upon the selection of `a parallel capacitor by means of switch 54.Alternative arrangements of my thermal regulator may be constructed byusing the alternative phase' shifting networks described in my copendingapplications Serial No. 770,968, now Patent No. 2,524,761, entitledPhaSe Shift System; Serial No. 770,966, now Patent NO. 2,524,759,entitled Phase Shift Network; Serial No. 770,967, now Patent No.2,524,760, entitled Phase Shift Bridge-all of these applications `beingtiled on August 28, 1947, and being issued on October l0, 1950.

'Ihe configuration of the phase shifting network embodied in FIGURE 4 ofthe subject application is similar to that shown in FIGURE 5 of patentapplication, Serial No. 779,909, now U.S. Patent 2,524,762, and itsvoltage vector diagram is similar to that shown in FiGURE 2 of saidpatent application, which is reproduced herewith as FIGURE 5. In FIGURE5, however, the voltage vectors have been renumbered to indicate thevoltages appearing across the corresponding elements in thephase-shifting network which is embodied in the thermal regulator shownin FIGURE 4. The transformer secondary 69 establishes a fixed voltagevector 68-64 having a center point 73 corresponding to the intermediatetap 73. The capacitor 70 and resistor 7l establish xed vectors E70 andE71 forming a right-angled triangle 662-64. IThe reactor 61 establishesa vector E51 extending from the fixed point 62 to the point 6o'. The sumor" the capacitors 52, 53 and of any additional capacitor selected byswitch 54 establishes a vector' EC extending from point l60 to fixedpoint 64'. Since the capacitors E?. and 53 are thermally sensitive, anychange of temperature will alter the length of vector Ec in relation tothe vector E61 which represents the reactor voltage, and this will causethe point 60 to travel around an arc as indicated by the dotted line inFIGURE 5. If the Q of the sum of the capacitors remains constant duringsuch temperature variation, or if it remains very high in comparisonwith the Q of the reactor, the phase angle between the vectors E61 andEc will remain constant and the arc will be the arc of a circle and itwill span the vector 62 and 64 as depicted in FIGURE 5; if the Q doesnot remain constant, the locus of point 66 will lie on an arc which isnot circular. In either event, however, the vector 73-6(', whichrepresents the output voltage of the thermal regulator, will rotateabout point '73', indicating that the output voltage will vary in phaseas the temperature changes. It will be noted that an increase incapacitance due to temperature change will shorten the vector MBL-64 andwill accordingly retard the phase of the output voltage 73 6t. It isalso evident that in the more generally known phase-shifting networks ofthe prior art, an increase in capacitance will retard the phase of thevoltage output vector, and I have therefore designated any suchphase-shifting network as having a normal sense of operation, incontrast to a special phase-shifting network which I shall describehereunder and which has an in verse sense of operation, for reasons tobe described later. In my thermal regulator, as shown in FIGURE 4, I mayuse a plurality of temperature-sensitive condensers 52 and 53 so thatthe phase angle may be regulated by an approximate average of thetemperatures at various points rather than by a single temperature but asingle temperature-sensitive condenser may be used for simplicity andeconomy if desired. Furthermore, I may connect a tixed or variablecondenser, such as the group 55, 56, 57 in parallel in order to vary thephase angle at a given temperature and so to vary the temperature atwhich a given phase angle results; however, this may also be omitted ifdesired, or alternatively such fixed capacitor may be connected inseries with the temperature-sensitive capacitor or capacitors.

The output of my thermal regulator is taken through conductors 72 and 74to an electric power controller 75 which may take the form of agrid-controlled rectifier tube 76 having a control grid 77 and a cathode78 to which conductors 74 and 72 are connected, respectively, through aresistor 79 and a filament transformer secondary 80 having a center tapat Si. A capacitor 82 is connected from grid 77 to ilament center tap Siand this may be variable, for the purpose of adjusting the phase angleof the control grid voltage, and therefore adjusting the desiredtemperature. The primary 83 of the filament transformer is connected topower input terminals 84, 85 which are connected in parallel with theinput terminals 67, 66 of thermal regulator 51. Power input terminal 34is connected through conductor 86 to the filament center tap 81. AnodeS7 of tube 76 is connected to a power output conductor 88, and powerinput terminal 35 is connected directly to power output conductor S9.Accordingly, the tube 76 acts as a rectifier to deliver a unidirectionalcurrent output to the conductors 8S and 39, the value of which isdependent upon the phase angle of the voltage applied between the grid77 and cathode 78 from the thermal regulator 51. It is easily understoodthat the connections to transformer 65 in the thermal regulator Sishould be made in the correct sense to ensure that, when the outputphase angle of the thermal regulator is fully retarded, the voltageapplied between grid 77 and cathode 78 is approximately 18() degrees outof phase with the voltage applied between anode 87 and cathode 78. Inorder to increase the average value of the unidirectional currentoutput, a large capacitor 9G is preferably connected across the outputconductors 8S and S9, preferably through a small series resistor 91, thepurpose of which is to limit the peak anode current of the tube 76 to asafe value.

A heat energy controller 92 comprises, in this instance, a device forcirculating air through heating and cooling coils 93 or 94, either ofwhich may be alternatively energized depending upon whether heating orcooling is required, the rate of circulation being determined by a fan95 which is driven by a variable speed motor having an armature 96 and afield winding 97, which are serially connected to the power outputconductors 8S and 89 of the electric power controller 75.

A source 9S of heat-containing medium at high temperature, such as hotwater or steam is provided for heating purposes. Alternatively, a source99 of heatcontaining medium at low temperature, such as a liquidrefrigerant is provided. Either one of these sources may be connected tothe heat energy controller 92, while the other source is shut off, bymeans of valves Nil and IGI. These valves may conveniently beelectrically operated through the medium of a thermostat M2 having abimetal strip 103 engaging alternative contacts 194 or 10S according towhether the temperature is below or above the desired value. Thermostat102 should be mounted in convenient relationship to thetemperature-sensitive capacitors 52 and 53. Alternatively, if a simplersystem is desired, either for heating only or for cooling only, one ofthe sources 98 or 99, together with its corresponding coil 93 or 94 maybe omitted. Even in such cases, however, it may be desirable to retainthe thermostat 103 to act as a limit control to cut otf the source ofheat-containing medium, and/or to cut off the electric power controllerin case a limiting hot or cold temperature should be exceeded. Theoperation of the entire system of FIGURE 4 will now be described forclarity.

In the case where a completely automatic heating and cooling system isrequired, the temperature-sensitive capacitors 52 and 53 are mounted atrepresentative points in the space or fluid or body which is associatedwith the heat energy controller and of which it is desired to controlthe temperature, for instance, on the inner and outer walls,respectively, of a room, or in diiferent rooms of a centrally heatedbuilding. The number of interconnected capacitors such as 52, 53 may beincreased to any desired extent and they may be connected in parallel orin series or in seriesparallel. For regulating the temperature of `aroom the temperature-sensitive dielectric of said capacitors is chosento have a Curie point, or temperature of maximum dielectric constant, ata comfortable temperature which is warm enough during winter and is yetcool enough in the summer, such for intsance as a temperature ofapproximately 75 degrees Fahrenheit, which corresponds with the Curiepoint of unconstrained Rochelle salt. The inductance of the reactor 61is then chosen so that when the temperature is close to the Curie point,for instance 72 degrees Fahrenheit in winter or 78 degrees Fahrenheit insummer, and when the thermally sensitive capacitors are therefore closeto their maximum capacitance, the phase angle of the output voltage "i3dof the thermal regulator 51 is sullciently retarded that, after it haspassed through the RC network 79-82 to the grid and cathode of tube 76,the output from the anode 87' and hence from the electric powercontroller 75 to the motor 95-97 is so low that the motor will not run;under these conditions there is a minimum flow of heat through the heatenergy controller 92.

The thermostat 102 is also adjusted to selectively open the valve 1d@(and close the valve 1&1) and so connect the heating source 98 to theheating coil 93 at all temperatures below the approximate Curie point,while at all temperatures above the approximate Curie point itselectively opens the valve 191 (and closes valve 163) and so connectsthe cooling source 99 to the cooling coil 94.

When the room temperature is, for instance, 72 degrees Fahrenheit, theheating coil 93 is connected to heating source 93 but the motor 96-97and fan 95 are stationary so that there is substantially no flow of heatinto the room. lf the room temperature now decreases to, say 7l degreesFahrenheit, the capacitance of the thermally sensitive capacitors 52, 53will decrease as shown in the section of the curve c-a in FIGURE 1 andthis will lengthen the capacitive voltage vector Ec in FIGURE 5 and soadvance the phase of the output voltage '7K-otr" of the thermalregulator, thus causing the tube 76 to deliver unidirectional current tothe motor @9e- 97 which thereupon drives the fan 95 and creates a liowof air past the heating coil 93. This establishes a flow of heat intothe room at a rate depending upon the rate of dow of air, and hence uponthe fan and motor speed. Since the temperature-sensitive capacitors arelocated in the room, the speed of the motor and hence the flow of heatwill be continuously modulated to maintain a substantially constant roomtemperature. It will be seen from FIGURE 1 that a small change intemperature causes a large change in capacitance. It will also be seenfrom FIGURE 5 that a small change in the length of the capacitivevoltage vector EC in relation to the inductive vector E6-L causes alarge change in phase angle of the output vector 732-611 and accordinglythe entire system is extremely sensitive, and I have found it possibleto maintain a temperature constancy of the order of l degree Fahrenheitwith cornparatively simple apparatus.

During hot weather, if the room temperature reaches, for example, 78degrees Fahrenheit, the thermostat 1&2 will have disconnected theheating coil 93 and will have connected the cooling coil 94 to the coldsource 99; under the conditions hereinbefore described, however, thephase of the thermal regulator output voltage will be so much retardedthat the motor and fan will not run, and there will be substantially noflow of heat. If the temperature should rise to say 79 degreesFahrenheit, the capacitance of the temperature-sensitive capacitors 52,53 will decrease as shown by the section c b of the curve in FIGURE land the phase of the thermal regulator output voltage will be advancedso that the tube 76 delivers power to the motor 96-97, thus driving thefan and forcing air through the cooling coils. rl`hus7 a flow of heat iscreated between the air and the cooling coils and the room is therebycooled and its temperature maintained substantially constant bycontinuous modulation of the rate of air flow and therefore of heat ow.

To allow for individual tastes in the degree of heating and coolingrequired, and to compensate for various conditions of rooms and ofwiring, etc., three adjustment means are provided in FIGURE 4 forselecting the relation between the motor speed and the amount by whichthe temperature differs from the Curie point. The first such meanscomprises switch 54 which may select an additional capacitor 55, 56 or57 to reduce the motor speed by steps, as desired, so that the regulatedtemperature is further from the Curie point as said capacitance isincreased. The second such means comprises the variable condenser 82 inconjunction with resistor 79. By increasing condenser 82 the phase ofthe thyratron grid voltage may be slightly retarded, and the motor speedsomewhat reduced, thus affording a ne continuous control of thetemperature to be regulated. I have also found it possible to adjust thephase angle and accordingly the operating temperature, when using adielectric of Rochelle salt, by adjusting the alternating current inputvoltage to the thermal regulator, as indicated by the adjustable tapping107 on the primary 65 of the input transformer for the thermalregulator.

The system described with reference to FIGURE 4 operates with a normalsense of control, as hereinbefore defined, inasmuch as the flow of heatis increased when the temperature varies away from the Curie point.FIGURE 4 embodies a phase shifter having a normal sense of control,inasmuch as a decrease in capacitance advances the phase of the outputvoltage. The electric power controller 75 of FGURE 4 may also be said tohave a normal senser of control, inasmuch as its output increases whenthe phase of the control voltage is advanced. Furthermore, the heatenergy controller 92 may also be said to have a normal sense of control,since the heat How is increased when its electrical input is increased.

FIGURE 6 illustrates a system having an inverted sense of control, whichis obtained by designing the heat energy controller to have an invertedsense of operation, while the phase shifter and the electric powercontroller each have a normal sense. The thermal regulator 121 comprisesa plurality of temperature sensitive capacitors 122, 123, 124 (though asingle such capacitor may be used if desired), which are connected inparallel with each other and to conductors 125, 126, which group ofcapacitors is connected in series with reactor 127 to alternatingcurrent input means 12S. An adjustable tap 129 is provided on reactor127 for the purpose of adjusting the desired operating temperature andto allow for the preferred number of temperature-sensitive capacitors ineach installation. The alternating current input means 128 comprises thesecondary 131i of transformer 131, across which the equal resistors 132,133 are serially connected through an output terminal 134. A xedcapacitor 135 and resistor 136 are also serially connected acrosstransformer secondary 130, and the circuit comprising reactor 127 andtemperature-sensitive capacitors 122, 123, 124 is connected across saidresistor 136. It will be seen that the thermal regulator 121 comprises atemperature-sensitive phase shifter similar in principle to thatillustrated in FIGURE 4, and its vector diagram is similar to that ofFIGURE 5, with appropriate changes to the numerals.

The output of thermal regulator 121 is taken from terminal 134 and fromtap 129 through conductors 137 and 138 to the opposite ends of seriallyconnected resistors 139, 140 which form the control circuit for anelectric power controller 141. Said electric power controller comprisesgrid-controlled rectifier tubes 142, 143 having anodes 144, 145energized from the secondary 146 of transformer 131, of which theprimary 147 is arranged for connection to an alternating current source148. The cathodes 149, 150 of tubes 142, 143 are heated by filamentsconnected to transformer secondary 151, which connections are omittedfor simplicity from FIGURE 6. The cathodes are connected to an outputconductor 152. The alternating current control voltage across resistors139 and 14d is applied to grids 153, 154 of tubes 142, 143 throughseries resistors 155, 156, also capacitors 157, 158 are connected fromgrids 153, 154, respectively, to conductor 152. The common point 120 ofresistors 139 and 14d is also connected to conductor 152. The output ofthe electric power controller 141 is taken from center tap 159 ontransformer secondary 146 to a conductor 160, and from conductor 152which is connected to cathodes 149, 150.

A heat energy controller 161 comprises a solenoidoperated valve 162, ahot Water boiler 163, a by-pass 164, a circulating pump 165, andradiation or convection piping and/or radiators 166 located in abuilding which it is desired to heat. The valve 162 is provided with anelectrically operated solenoid 167 which is connected through terminals168, 169 to conductors 169 and 152. The valve also comprises a body 171ihaving alternative inlet ports 171, 172, and an outlet port 173. Aslidable plunger 174 is provided with piston portions 175, 176, and withan armature portion 177. The armature comprises a magnetic materialwhile the remaining valve parts are preferably non-magnetic. A spring17S is compressed by an end cap 179 so as to force the plunger 174 tothe left, thus opening port 171 and closing port 172, in the absence ofany electrical input at terminals 168, 169. Under these conditions, hotwater from boiler 163 is forced by circulating pump 165 through piping166 and heat is transferred to the building at the maximum rate. Whenelectrical energy is supplied to terminals 168, 169, however, thearmature 177 is pulled towards the right, thus progressively closingport 171 and opening port 172 as the electrical input is increased, andaccordingly permitting an increasing percentage oi the water to owthrough by-pass 164 instead of through boiler 16S, and thus reducing therate of heat transfer to the building.

In the operation of the entire system, one or more of thetemperature-sensitive capacitors 122, 123 are located within thebuilding of which it is desired to control the temperature, and theirCurie point is chosen to be below the lowest desired temperature. As thetemperature within the building rises, the capacitance of saidtemperature-sensi-tive capacitors decreases, thus advancing the phase ofthe voltage applied to grids 153, 154 of electric power controller 1li-1and increasing its output to conductors 16), 162. Accordingly thesolenoid 167 is energized to an increasing extent, thus moving plunger174 of valve 162 to the right, and by-passing the flow of water so as toreduce the rate of heat transfer to the building until such time as thetemperature reaches a stable value at which the temperature-sensitivecapacitors provide the appropriate phase shift to give the necessaryrate of heat flow.

lt will be seen that this system has an inverted sense of control,inasmuch as the flow of heat decreases when the temperature varies awayfrom the Curie point.

1f it is desired to compensate for variations in outdoor temperature oneof the thermally sensitive capacitors 124 may be mounted outdoors,providing its capacitance is suitably low compared with the totalcapacitance of those rwhich are -mounted indoors. chosen to be below theminimum expected outdoor temperature so that it operates in the sameinverted sense as the indoor capacitors.

The adjustable tapping 129 on reactor 127 provides a means for adjustingthe desired operating temperature by changing the inductance of 127 sothat a different capacitance, and therefore a ditferent temperature, isrequired to produce a given phase angle at the output conductors 137,138 of the thermal regulator '121.

FIGURE 7 illustrates a system in which an inverted Asense of control isobtained by means of a special phaseshifting network having an invertedsense, together with an electrical power controller and a heat energycontroller each having a norma sense of control. The thermal regulator181 is provided with input terminals 182, 133 for connection to analternating current source 184. A capacitor 165 and a resistor 186 areserially connected between input terminals 162, 183, Aternperature-sensitive capacitor 137 is provided with a its Curie pointshould be 1 9 A temperature-sensitive dielectric 1S@ and with twoelectrodes connected to terminals 133, 169 which are connected in Serieswith reactor 1%- across a portion of resistor 186 between an endterminal 191 and a tap 192.

The temperature-sensitive capacitor 167 is also provided with a heaterwinding 193 connected to terminals 194, 195 which are in turn connectedacross an adjustable portion of a resistor or transformer 196 which isconnected to a suitable current source at 197, 198.

The elements 165, 186, 187, 190 comprise a phaseshifting network havingan inverse sense of operation inasmuch yas a decrease in capacitance `of187 will retard the phase angle of the voltage appearing at the outputterminals 199 and 197 as will be seen from the vector diagram reproducedin FIGURE 8.

Referring to FIGURE 8, the vector 197198 represents the input voltagefrom the alternating current source. Vector 19T-191 represents theVoltage across capacitor and a vector 19T-19S' represents the voltageacross resistance 186, on which 192' represents the potential of tappingpoint 192. The vector 1912-192' represents a reference voltage, acrosswhich reactor and temperature-sensitive capacitor 167 are seriallyconnected. Vectors 191199 and 19V-192 represent the voltages acrossreactor 19t) and temperature-sensitive capacitor 187, respectively, asthey exist when the capacitance of 187 is high, corresponding to atemperature approaching the Curie point. As the temperature moves awayfrom the Curie point, the capacitance of 137 decreases, resulting in alengthening of the capacitive voltage vector 199'-192 in relation to theinductive vector 19h-199' and the point 199' then moves counterclockwiseround an arc such as the arc A shown in dotted lines, which spans thereference voltage vector 191-192, to a new point such as 199. The outputvoltage is taken between the variable point indicated by 199' or 199,and the fixed point 197 and since the point 197 is outside the arc A itwill be seen that when point 199 moves counterclockwise around the arc,the output vector 19T-129' moves clockwise. Accordingly, the phaseshifter operates in an inverse sense and a decrease in capacitancecauses a clockwise rotation of the output vector corresponding to aretardation in phase angle.

Continuing the description of FIGURE 7, the output terminals 197 and 199of the thermal regulator 131 are connected through conductors 261), 201to the cathode 2112 and grid 203 of the space discharge device 264,which also has an anode 265 and which acts as the electric powercontroller 296.

A resistor 207 and a capacitor 208 are provided in the grid circuit toby-pass unwanted transients. The device 204 is filled with suitable gasor vapor and the cathode 202 may be heated by a iilament, not shown, orit may be a cold cathode with means, not shown, for establishing andmaintaining a space discharge from the cathode. Conductors 260 and 209act as input leads to electric power controller 206, while conductors210, 211 act as output leads which are connected to the series field 212and armature 213 of a motor forming part of the heat energy controller214. Said heat energy controller comprises a mechanical Stoker 215 whichincludes a fuel hopper 216, a tuyere or burner 217, and an Archimedeanscrew feed 21S which is driven from motor armature 213 and gearing 219,220. A heating furnace is instailed above the tuyere 217, together withmeans for distributing its heat output to a building, these elementsbeing omitted for simplicity, but the temperature-sensitive capacitor187 is installed within said building for the purpose of regulating itstemperature.

The dielectric 186 of said temperature-sensitive capacitor 187 has aCurie point which may be at the approximate temperature which it isrequired to control, such as Rochelle salt, having a Curie point atabout 75 degrees Fahrenheit. The heating resistor 193 is arranged toraise the temperature of the dielectric 180 of capacitor 187 to atemperature somewhat above the desired room ternperature, and theconstants of the reactor 190` and of the remaining components of thermalregulator 181 are adjusted so that when the room temperature is at thedesired value and the dielectric 180 is at a temperature convenientlyabove the Curie point, such as 80 degrees or 85 degrees Fahrenheit, themotor armature 213 is running at a speed sufficient to feed the requiredamount of fuel to the furnace. Any increase in room temperature willthen decrease the capacitance of 187, thus retarding the phase of theoutput voltage from thermal regulator 181, so reducing the output ofelectric power controller 206 and slowing down the motor armature 213and reducing the rate of fuel supply to the tuyere 217, and vice versa.

In order to reduce the desired temperature of the building, thepotentiometer or transformer 196 is adjusted to deliver more current toheater 193, thus increasing the difference between the room temperatureand the temperature at which the dielectric 130 is automatically andconstantly maintained, thus depressing the room temperature, and viceVersa.

Another method of controlling the desired temperature is illustrated inFIGURES 9 and 10. FIGURE 9 is reproduced from The Iournal of theInstitution of Electrical Engineers, volume 93, Part I, No. 72, December1946, page 595, Figure A, and this shows the variation of dielectricconstant of a barium-strontium titanate versus temperature when a directcurrent voltage gradient is superimposed on the dielectric. It will beseen that the temperature at which a given dielectric constant isobtained may be altered by superimposing direct current voltagegradients of different values. For instance, cur-ve 231 shows thevariation of dielectric constant versus temperature when no directcurrent voltage gradient is applied. Curve 232 shows such variation whena direct current Voltage gradient of G00 volts per centimeter isapplied. Curve 233 shows such variation when a direct current voltagegradient of 10,000 volts per centimeter is applied. It will be seen thata dielectric constant of 2500 is obtained at approximately 96 degreescentigrade for curve 231, 100 degrees centigrade for curve 232 and 104degrees centigrade for curve 233.

FIGURE l0 shows a modification to the circuit shown in FIGURE 6 in whicha direct current voltage is applied to the temperature-sensitivecapacitor 246 by means of a direct current source shown diagrammaticallyas a rectier 241 which is supplied with alternating current from atransformer secondary 242 having an adjustable tapping 243, and whichdelivers a unidirectional current to the large capacitor 244. A directcurrent voltage is accordingly developed across capacitor 244 and isapplied, through resistor 136 and reactor 127 to conductors 125, 126 andthence to a temperature-sensitive capacitor 246. Accordingly the directcurrent voltage gradient in the temperature-sensitive dielectric 245 maybe adjusted by means of the adjustable tapping 243 so as to vary thetemperature at Which a given dielectric constant is obtained, and thusto vary the temperature which it is desired to control. The dielectric245 is preferably very thin so that the direct current voltage requiredis not excessively high and said dielectric may take the form, forinstance, of a ceramic coating applied to an electrode 247 and/or anelectrode 248.

FIGURE 11 shows an alternative form of heat energy controller in whichheat is created by the electrical output from the electric powerconverter or controller. The vessel 251 contains a liquid 252 which isheated by an energy-delivering device in the form of an electricalheating resistor 253 which is connected through conductors 254, 255 tothe output of an electric power converter or controller, such as thatshown in FIGURES 4, 6 or 7.

The mechanical stirrer 256 is provided to improve the uniformity ofheating of the liquid. Temperature-sensitive capacitors 257, 258 and 259have been provided, any one of which may be selected by a switch 260 andconnected to conductors 261 and 262 so as to form a part of a thermalregulator such, for instance, as that shown in FIGURE 4 in which caseconductors 261 and 262 replace conductors 58 and 59 of FIGURE 4, or suchas that shown in FIGURE 6 or FIGURE 7. A protective shield or casing 263is preferably provided to protect the temperature-sensitive capacitorsfrom the liquid 252. The temperature of the liquid 252 is continuouslycontrolled by the variation in capacitance of whichevertemperaturesensitive capacitor is selected by switch 260 and the systemautomatically maintains a substantially constant desired temperature.The desired temperature value may be varied over a given range by theVarious means described in reference to FIGURES 4, 6, 7 or 10. Thedesired temperature may be further adjusted by arranging thetemperature-sensitive capacitors 257, 258, 259 to have diierent Curiepoints and/or different capacitances, any one of which may be selectedby switch 260.

FIGURE 12 shows a heat energy controller of a form in which heat iscreated as an unwanted by-product, and it is desired to control thetemperature rise resulting therefrom. The vessel 271 may, for instance,comprise the casing of a storage battery or an electrolytic cellcontaining a liquid electrolyte 272 in which plates or electrodes 273and 274 are immersed, and are connected by conductors 275 and 276 to theoutput of an electric power controller such as is shown in FIGURES 4, 6or 7. A temperature-sensitive capacitor 277 which is provided with aprotective coating or casing 278 is also immersed in the liquid 272 andis connected by conductors 279, 280 to` circuits, such as those shown inFIGURES 4, 6, or 7 to constitute a complete thermal regulator.Accordingly if the temperature of the liquid -272 exceeds a desiredvalue the output of the electric power converter or controller isprogressively reduced by the action of the thermal regulator so as tolimit the temperature rise.

FIGURE 13 illustrates another form of heat energy controller `in whichheat is created as an unwanted byproduct in the treatment of a materialby ultrasonic energy. A liquid 291 to be treated ultrasonically iscontained in a vessel 292 and ultrasonic energy is transmitted .to theliquid through the wall 293 of vessel 292 from the second liquid 294which is contained Within the vessel r295 and which is maintained athigh pressure by a pump connected to the port 296. Ultrasonic energy isdeveloped in liquid 294 by means of the ultrasonic transducer 297 whichmay comprise, for instance, a piezoelectric or magnetostriction vibratorhaving electrodes or terminals 298, 299 which are energized by a highfrequency current supplied through conductors 300 and 301 from anelectric power converter or controller, such as shown by the block 33 inFIGURE 3. In this instance, however, the electric power converter orcontroller is designed to deliver a high frequency alternating currentinstead of a unidirectional current.

Temperature-sensitive capacitor 302 which may be provided With aprotective coating or casing 303 is connected by conductors 304 and 305to circuits, such as those shown in FIGURES 4, 6 and 7, to constitute acomplete thermal regulator for controlling the output of the electricpower converter or controller, and thereby controlling the electricalpower input to the transducer 297 so that said power output isprogressively reduced after a desired limiting temperature has beenreached; in this way for instance the maximum amount of ultrasonicenergy may be propagated through the liquid 291 without reaching itsboiling point.

Since the temperature-sensitive capacitor 302 will be subjected toultrasonic bombardment, an unwanted high frequency voltage may bedeveloped due to piezoelectric effect in its dielectric. Accordingly,the dielectric is preferably made in the form of a sandwich comprisingtwo layers of dielectric material 306 and 307, which are of equalthickness but which are so prepared and oriented that equal and oppositehigh frequency voltages will be developed in each layer so that thetotal high frequency voltage appearing across the two layers in seriesapproximates to zero. Electrodes 303 and 309 are provided at the outerfaces of each layer and are connected to the conductors 365 and 364, andan additional common electrode or pair of adjacent contacting electrodes310 may be provided between the two layers. A closure 311 is preferablyprovided at the top of vessel 292 to prevent escape of the liquid 291while under bombardment.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

l. A system for charging a storage battery at a rate which is limited bythe safe battery temperature comprising: a phase-sensitive controlledrectifier provided with alternating current input means and directcurrent output terminal means for connection to said battery, and atleast two phase-sensitive control terminals; a temperaturesensitivephase-shifting device comprising an input network energized from saidalternating current input means, at least one capacitor having atemperature-sensitive ferroelectric dielectric and adapted to be placedin heat-receiving relationship with said battery, an inductance seriallyconnected with said capacitor across said input network with a rstoutput terminal operatively connected between said capacitor and saidimpedance, and a second output terminal connected to a point on saidinput network; and connections from the output terminals of saidphase-shifting device to said control terminals.

2. A system as set forth in claim l, in which the capacitor having thetemperature-sensitive dielectric is immersed in the electrolyte of saidstorage battery.

3. A system as set forth in claim 2, in which the capacitor is providedwith a protective shield adapted to be at least partially immersed insaid electrolyte.

4. A system for regulating the temperature of an electrolyte fluid,comprising an electrode means immersed in said electrolyte fluid; aphase-sensitive electric power converter for supplying variable electricpower to said electrode means; alternating current input means; atemperature-sensitive passive phase-shifting network including at leastone capacitor having a temperature-sensitive ferroelectric dielectricand an inductive element in series with said capacitor, said capacitorbeing disposed in said fluid and connected to said input means fordelivering a continuously maintained output, the phase angle of which iscontinuously variable in accordance with the capacitance of saidcapacitor; said phase-sensitive converter being ltd connected to theoutput of said network, said input meansi said converter and saidelectrode means being operatively intereoupled whereby the flow ofelectric power to said electrode means is continuously controlled by theternperature of said temperature-sensitive capacitor.

5. A system as set forth in claim 4, in which the temperature-sensitivecapacitor is located within a protective shield and immersed in theelectrolyte.

6. A system for regulating the temperature of a storage batteryelectrolyte, comprising electrode plates of a storage battery disposedin said storage battery electrolyte; a phase-sensitive electric powerconverter for supplying variable electric power to said plates;alternating current input means; a temperature-sensitive passivephase-shifting network including at least one capacitor having atemperature-sensitive ferroelectric dielectric and an inductive elementin series with said capacitor, said capacitor being disposed in saidiluid and connected to said input means for delivering a continuouslymaintained output, the phase angle of which is continuously variable inaccordance with the capacitance of said capacitor; said phase-sensitiveconverter being connected to the output of said network, said inputmeans, said converter and said plates being operatively intercoupledwhereby the flow of electric power to said plates is continuouslycontrolled by the temperature of said temperature-sensitive capacitor.

7. A system for regulating the temperature of a fluid, comprising adevice adapted to generating energy in a predetermined non-thermal formas well as in the form of undesired thermal energy deposited in saidfluid; a phase-sensitive electric power converter to said device;alternating current input means; a temperature-sensitive passivephase-shifting network including at least one capacitor having atemperature-sensitive ferro-electric dielectric andan inductive elementin series with said capacitor, said capacitor being disposed in saidfluid and connected to said input means for delivering a continuouslymaintained output, the phase angle of which is continuously variable inaccordance with the capacitance of said capacitor; said phase-sensitiveconverter being connected to the output of said network, said inputmeans, said converter and said device being operatively intercoupledwhereby the flow of electric power to said device is continuouslycontrolled by the temperature of said temperature-sensitive capacitor,and the system operates to limit the maximum temperature of the fluid.

References Cited in the tile of this patent UNITED STATES PATENTS2,017,859 Halstead Oct. 22, 1935 2,498,814 Little et al Feb. 28, 19502,505,565 Michel et al Apr. 25, 1950 2,568,435 Downey Sept. 18, 19512,673,917 Woodling Mar. 30, 1954 2,842,345 Brown July 8, 1958 2,887,646Gilchrist May 19, 1959 2,898,543 Roper et al Aug. 4, 1959

